Lift induced wingtip vortices account for 25 to 40 percent of total airframe drag on fixed-wing transport aircraft, which poses a longstanding challenge in aircraft design. Recent efforts to reduce this drag loss include distinct wingtip structure, for example U.S. Pat. No. 7,900,876 to Eberhardt describes sets of wingtip feathers with respective forward and aft sweep angles. Prior efforts to both reduce vortex drag and recover a portion of the otherwise lost vortex energy disclose the use of non-powered wingtip mounted turbines that extract energy from the vortex, for example U.S. Pat. No. 2,485,218 to Shaw, U.S. Pat. No. 4,428,711 to Archer, U.S. Pat. No. 4,917,332 to Patterson, U.S. Pat. No. 5,100,085 to Rubbert, U.S. Pat. No. 5,150,859 to Ransick, U.S. Pat. No. 5,702,071 to Curran and Kroll, U.S. Pat. No. 5,918,835 to Gerhardt, U.S. Pat. No. 5,934,612 to Gerhard, and NASA Technical Paper 2468 published June 1985 by J. C. Patterson, Jr. and S. G. Fletcher, “Exploratory Wind-Tunnel Investigation of a wingtip-Mounted Vortex Turbine for Vortex Energy Recovery”. Also see U.S. Pat. No. 3,596,854 to Haney and U.S. Pat. No. 2,477,461 to Lee. In the related field of wind energy conversion, means to convert induced vortex energy from non-rotating structures is disclosed in U.S. Pat. No. 4,045,144 to Loth, U.S. Pat. No. 4,105,362 to Sforza, and U.S. Pat. No. 7,131,812 to Brueckner.
The prior art also describes the use of powered wingtip devices that both provide propulsion and dissipate vortex drag. For example, U.S. Pat. No. 3,997,132 to Erwin describes supplemental wingtip mounted jet engines with controllable fins that swirl their exhaust streams in opposition to the vortices. U.S. Pat. No. 4,533,101 to Patterson discloses a pusher type propeller with radial blades mounted downstream of the wing tips, where the propellers rotate in opposition to the vortices. Vortex cross-flow thereby increases relative airspeed through the propellers and turns the resultant lift vectors upstream. This both increases propulsive force and weakens the vortex, and downstream injection of the propeller wake into the vortex further weakens the vortex. Lastly, patent application PCT/EP2012/074376 by Lopez and Schneider describes wingtip propellers deployed within wingtip slots.
The present invention employs a wingtip mounted pusher type fan for primary propulsion, which turns in opposition to the vortex rotation direction following Patterson in U.S. Pat. No. 4,533,101. Here the improvement in propulsion efficiency comprises a novel wingtip nacelle form and a novel pusher fan design. The pusher fan is distinct from Patterson because its outward-aft blade sweep angle directs convergent backwash to a central high pressure flow volume that more efficiently dissipates the cyclonic structure of the vortex.
In an alternative horizontal axis wind turbine embodiment, the same nacelle form supports secondary power-takeoff turbines mounted in high energy density flow at the turbine blade tips. In this arrangement, the secondary turbines turn in the same direction as the lift induced vortices. This reduces blade tip vortex drag and directly generates additional electrical power. The same embodiment is adaptable to large scale power generation from tidal, river, and ocean currents.
The primary purpose of the present invention is to improve the efficiency of energy expenditure in powered flight. The secondary purpose is to dissipate vortices that trail wingtips of large aircraft to reduce wake turbulence that is hazardous to other aircraft. In the alternative embodiment, the primary purpose is to improve the efficiency of fluid kinetic energy capture.